JunOS IPv6 announcements over IPv4 BGP

David Swafford david at davidswafford.com
Sat Dec 22 02:50:24 UTC 2012

One reason that may force others down this track comes from exceeding
the # of configurable BGP sessions on a box (think chassis switches).
It does add a good bit of complexity in the initial roll-out  but it's
really not all that bad once you get used to it.  The one piece that
seems to make it a little easier is that you get a consolidated view
on some devices, where the prefix counts are shown for both address
families under the same "show ip bgp neighbor" display.


On Fri, Dec 21, 2012 at 3:04 PM, Leo Bicknell <bicknell at ufp.org> wrote:
> In a message written on Fri, Dec 21, 2012 at 11:45:24AM -0700, Pete Ashdown wrote:
>> I've got a peer who wishes me to send my IPv6 announcements over IPv4 BGP.
>> I'm running around in circles with JTAC trying to find out how to do this
>> in JunOS.  Does anyone have a snippet they can send me?
> A believe you got the snippet, but I wanted to expand on why this
> is a bad idea.  From a protocol perspective, BGP can create one
> session over a particular transport (IPv4, or IPv6 typically) and
> then exchange routes for multiple address families (IPv4 unicast,
> IPv4 multicast, IPv6 unicast, IPv6 multicast, or even all sorts of
> fun MPLS stuff).  From a network management perspective doing so
> can complicate things immensely.
> Today networks want to deploy IPv6 without impacting their IPv4
> network.  Adding IPv6 AFI to an IPv4 transport session will tear
> it down, impacting IPv4 customers.
> Tomorrow, when IPv4 transport fails, IPv6 customers are also impacted
> by the failure of the transport, even though there may be no IPv6
> routing issues.  There is also a chance that IPv6 forwarding fails, but
> the routing information lives on running the traffic into a black hole
> since the routing information isn't sharing the failed transport.
> In the future, IPv4 will be removed from the network.  If all of
> the transport is IPv4, those sessions will have to be torn down and
> new ones built with IPv6 transport before the IPv6 only network can
> live on.
> I believe the vast majority, approaching 100% of larger ISP's move
> IPv4 routes over IPv4 transport, and IPv6 routes over IPv6 transport,
> treating the two protocols as ships in the night.  It elminates all
> three problems I've listed above at the grand expense of your router
> having to open/track 2 TCP connections rather than one; a trivial
> amount of overhead compared to the routes being exchanged.
> Of course, there are people who like to be different, sometimes for good
> reasons, often not... :)
> --
>        Leo Bicknell - bicknell at ufp.org - CCIE 3440
>         PGP keys at http://www.ufp.org/~bicknell/

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